Conventional processes for the production of solid Fe(III) chelates for agricultural and other uses generate waste crystal liquors with high concentrations of iron and heavy metals, particularly chromium. Such heavy metals are problematic from an environmental standpoint. The economic implications of properly disposing of such streams are significant, and are often prohibitive. In addition, the waste liquor can contain some soluble product. Although disposal of the waste liquors without recovering the product results in yield loss, recovery of contained product is not economical.
A conventional process for producing the complexes involves reacting chelating agents, such as EDTNa.sub.4 or DTPANa.sub.5, with ferric chloride solution, followed by filtration, washing and drying. However, one major source of chromium contamination is the ferric chloride used as the ferric iron source. Where low cost grade ferric chloride derived from scrap iron is used, the chromium concentration of the waste streams produced is on the order of 30 ppm. Higher grade ferric chloride can be used, which can reduce the chromium concentration in the waste streams to about 2-3 ppm; however, this higher grade ferric chloride is more expensive. A further drawback of ferric chloride is the highly corrosive properties of the slurries and liquors produced from the chelating agent/ferric chloride reactions.
Prior art drying processes include spray drying and drum drying. However, the resulting product is often very dusty, which creates handling problems. Accordingly, there is a need to find an alternative production process which reduces or eliminates the generation of high heavy metal effluents without adding significant cost.
Fertilizer formulations often contain secondary nutrients or micronutrients. These are metals, usually in the form of metal complexes. EDTA is the most commonly used chelating agent and the major micronutrient metals are iron, copper, manganese and zinc. Several other metals are also used as micronutrients in such formulations, including boron, molybdenum and cobalt. Secondary nutrients are calcium and magnesium. The major components of fertilizer formulations are potash, phosphate and nitrogen compounds. To prepare these formulations, the components are blended. This operation requires adding to the blender the major components plus very small amounts of two or more micronutrients or secondary nutrients, each of which must be precisely weighed and thoroughly blended. The blending operation could be simplified and made more efficient if a single mixture of all the micronutrients and secondary nutrients were available as a single blend. One object of this invention is to provide such a blend.